Conventionally, in blood sampling, a blood component sampling in which only platelets and the like are collected and other components are returned to the blood donor (donor) is mainly employed, and at the time of the blood component sampling, a blood component separation device equipped with a centrifugal separator is used.
In recent years, blood transfusion with a platelet liquid is widely conducted in radiation therapy of cancer or the like, and in such a case, a high concentration of platelet liquid is required. For collecting a high-concentration platelet liquid, the technique of Patent Literature 1 collects a target number of units of platelets by conducting a platelet collecting calculation for separating blood sampled from a blood donor and collecting platelets in multiple cycles.